The present invention relates to an air filtration and cleaning system for enclosures and more particularly to such a system particularly adapted for indoor gun firing ranges. Indoor gun firing ranges present particular problems for indoor air quality as well as the quality of air exhausted to ambient outdoor air. Standards for lead exposure and air quality have been developed by the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) as well as state and local air quality and environmental protection authorities. Laws and regulations have been established which present new compliance requirements and difficulties for owners and operators of such indoor range facilities. These standards provide specific guidelines to ensure that contaminants present in indoor firing ranges are properly controlled to ensure the safety of the shooter, employee and other persons who may be present within the range area. Further, the standards provide specific guidelines to ensure that contaminated air is not discharged into the atmosphere, but that contaminant levels are reduced to minimally acceptable levels. Indoor gun ranges present particularly difficult problems, because, as noted in U.S. Pat. No. 4,164,901, the following chemical elements are released into the atmosphere: boron, sodium, aluminum, silicon, phosphorus, sulphur, chlorine, potassium, calcium, titanium, chromium, manganese, iron, nickel, copper, zinc, arsenic, selenium, silver, cadmium, antimony, telrium, mercury, thallium, bismuth, lead solids and lead oxides as well as unburned gun powder and carbon monoxide gas. Certain of these elements are toxic, and continued exposure to them, as by a range employee, may lead to health problems or even death. Moreover, these contaminants cannot be released safely into the outside air.
Most existing indoor gun ranges have poorly designed ventilation systems, and either no or limited filtration such that at the present time few, if any, ranges comply with existing clean air standards. While Clean Air Act administrators on federal, state and local levels have not heretofore been active in ensuring compliance by gun range operators, administrators have been advising the operators that compliance will be necessary and monitored.
Additionally, the same or similar conditions which contaminate the air in gun ranges are also present with respect to other industrial processes. For example, metal plating operations are well recognized sources of contaminated air, as are radiator repair and other lead uses, including certain flux cleaning operations such as in the production of printed circuit boards and other electronic operations. Other industries or practices which produce contaminated air include biochemical operations or medical laboratories. Some such operations employ a "clean room" technique which circulates air through filters and which maintain a slight overpressure within an enclosed area. Greater than ambient pressure, or overpressure, is particularly hazardous when contaminants are involved, because overpressure within an enclosed area forces contaminants out of the room rather than creating a negative or underpressure within the room which would pull outside air in.
Others have attempted to respond to the problem of contaminated air within an indoor firing range by employing various air duct systems and filtration methods. For example, U.S. Pat. No. 4,164,901, assigned to American Air Filter Company, Inc., is directed to an indoor gun firing range enclosure for removing contaminants from the air, but still exhausts 80% of the air volume of the indoor chamber to the outside after being filtered. The method of filtration is such that filtration is arguably incomplete and would fail to meet current Clean Air Act standards. Older systems are also energy inefficient. Additionally, the system described in the '901 patent pulls air from one end of the range to the downrange end so that the shooter is constantly standing in an uncomfortable draft. The practice disclosed in the '901 patent demonstrates the problems of providing a safe, clean and comfortable environment for the shooter which can be in conflict with the necessity to comply with Clean Air Act standards.